DS2790 Datasheet, PDF (9/41 Pages) Maxim Integrated Products – Programmable 1-Cell Li-Ion Fuel Gauge and Protector

DS2790 Programmable 1-Cell Li-Ion Fuel Gauge and Protector
DETAILED DESCRIPTION
The following is an introduction to the primary features of the DS2790 Programmable 1-Cell Li-Ion Fuel Gauge and
Protector. More detailed descriptions of the device features can be found in the errata sheets, and user's guides
described later in the Additional Documentation section.
DS2790 Overview
The DS2790 incorporates the 16-bit MAXQ20 microcontroller core with 16 accumulators and 16-level hardware
stack. Four memory blocks provide application code space, utility code space, RAM memory, and EEPROM
memory. Specialized peripherals are integrated to perform battery monitoring, coulomb counting, Lithium-Ion
protection, and 2-wire communication functions. The MAXQ20 core along with the specialized peripherals provide
a flexible solution for fuel gauging and protection of Lithium-Ion battery packs. Flexibility is further enhanced as the
solution allows for upgrading of the program and data EEPROM contents over the 2-wire interface. Updates to the
program and data EEPROM are protected against unauthorized writes by a 256-bit user password. A read
protection bit is provided to prevent reading either EEPROM.
MAXQ20 Core Architecture
The DS2790 employs a MAXQ20 low-cost, high-performance, CMOS, fully static, 16-bit RISC microcontroller with
EEPROM memory. It is structured on a highly advanced, 16 accumulator-based, 16-bit RISC architecture. Fetch
and execution operations are completed in one cycle without pipelining, since the instruction contains both the op
code and data. The highly efficient core is supported by 16 accumulators and a 16-level hardware stack, enabling
fast subroutine calling and task switching. Data can be quickly and efficiently manipulated with three internal data
pointers. Multiple data pointers allow more than one function to access data memory without having to save and
restore data pointers each time. The data pointers can automatically increment or decrement following an
operation, eliminating the need for software intervention.
Instruction Set
The instruction set is composed of fixed-length, 16-bit instructions that operate on registers and memory locations.
The instruction set is highly orthogonal, allowing arithmetic and logical operations to use any register along with the
accumulator. Special-function registers control the peripherals and are subdivided into register modules. The family
architecture is modular, so that new devices and modules can reuse code developed for existing products
The architecture is transport-triggered. This means that writes or reads from certain register locations can also
cause side effects to occur. These side effects from the basis for higher-level op codes defined by the assembly,
such as ADDC, OR, JUMP, etc. The op codes are implemented as MOVE instructions between certain register
locations, while the assembler handles the encoding, which need not be a concern to the programmer. The 16-bit
instruction word is designed for efficient execution.
Bit 15 indicates the format for the source field of the instruction. Bits 0 to 7 of the instruction represent the source
for the transfer. Depending on the value of the format field, this can either be an immediate value or a source
register. If this field represents a register, the lower four bits contain the module specifier and the upper four bits
contain the register index in that module.
Bits 8 to 14 represent the destination for the transfer. This value always represents a destination register, with the
lower four bits containing the module specifier and the upper three bits containing the register subindex within that
module. Any time that it is necessary to directly select one of the upper 24 registers as a destination, the prefix
register PFX is needed to supply the extra destination bits. This prefix register write is inserted automatically by the
assembler and requires only one additional execution cycle. See the MAXQ Family User's Guide for complete
instruction set information.
9 of 41